The current objective of these studies has been the application of physical and biochemical techniques to characterize the length and structure of inverted terminal repeats (ITR's) in the genomes of both oncogenic and nononcogenic human adenoviruses (Ad). Our ultimate goal is to define the roles of these sequences in regulating viral and cell growth (e.g., infectious yield and efficiency of cellular transformation). We have now described several important structural features of Ad ITRs (i.e., size, variations and homologies). Among methods used are gradient sedimentation, DNA cleavage with restriction endonucleases, gel electrophoresis, base sequence analysis and electron microscopy.